TCP performance analysis and optimization over DMT based ADSL systems

This paper studies the transmission control protocol (TCP) performance over a discrete multi-tone (DMT) based asymmetric digital subscriber loop (ADSL) network. The impact of DMT subchannel bit loading on the TCP throughput performance is studied. The simulation results show that there is a threshold for the signal-to-noise ratio (SNR) gap or bit error rate (BER) above which TCP throughput drops quickly. This threshold takes its value in a wide range depending on the TCP round-trip time as well as channel noises. This suggests that it would be insuf®cient to set a ®xed target BER at, e.g. 10, when calculating the number of bits to be loaded in each subchannels. Instead, the bit loading should take TCP performance into account. Finally a dynamic bit loading scheme is proposed, which jointly optimizes the channel bit rate and TCP throughput performance. q 2001 Elsevier Science B.V. All rights reserved.